1. Field of the Invention
The present invention relates to an extrusion molding machine for extruding a ceramic molding.
2. Description of the Related Art
For instance, a known catalyst carrier for an exhaust gas purifier for an automobile is comprised of a ceramic honey-comb structure 8 having a number of cells 88 spaced by separation walls 81, as shown in FIG. 19. In general, a ceramic molding such as the ceramic honey-comb structure 8 is formed by extrusion molding. Moreover, the extrusion molding can be also used to form a sheet-like ceramic product, i.e., a ceramic sheet.
A conventional extrusion molding machine 9 is comprised of, for example, a molding die 11 for forming the ceramic molding 8, and two-stage screw extruders 2 and 3 for continuously kneading and extruding the ceramic material 80, as shown in FIG. 17. Note that the two-stage screw extruders can be replaced with a single-stage screw extruder or more than two-stage screw extruders.
As can be seen in the drawing, the screw extruders 2 and 3 are respectively provided with housings 21 and 31 which define material passageways 20 and 30 in which screws 22 and 32 having shaft portions 221 and 321 and helical leads 222 and 322 formed therearound extend.
A material introduction portion 93 through which the ceramic material 80 is introduced is provided above the rear end of the upper stage screw extruder 3. The material introduction portion 93 is provided with a hopper 939 through which the material is fed and a pair of right and left feed rollers 931. As shown in FIG. 18, the right and left feed rollers 931 are opposed to each other and are rotated in opposite directions (in the downward direction at the opposed surface portions), so that the ceramic material 80 dropped onto the feed rollers 931 is forced between the feed rollers 931 and fed downward.
As shown in FIG. 17, in case of the two-stage screw extruders 2 and 3, a vacuum chamber 5 is provided between the screw extruders. The vacuum chamber 5 is adapted to degas the ceramic material 80 which has been kneaded by the upper stage screw extruder 3 and to feed the ceramic material 80 having a high bulk density to the lower stage screw extruder 2. The vacuum chamber 5 is also provided therein with a pair of right and left feed rollers 921 similar to those of the material introduction portion 93, so that the ceramic material 80 can be fed to the lower stage screw extruder 2.
To produce the ceramic molding 8 using the extrusion molding machine 9, the ceramic material 80 which is not kneaded is charged into the material introduction portion 93 from the hopper 939, as shown in FIG. 17. The ceramic material 80 is forced between the pair of right and left feed rollers 931 in accordance with the rotation thereof and is fed into the screw extruder 3.
Thereafter, the ceramic material 80 is fed forward while being kneaded by the upper stage screw extruder 3 and is discharged from the front end thereof into the vacuum chamber 5. Thereafter, the ceramic material 80 which has been kneaded to some extent is degassed in the vacuum chamber 5 and is fed into the lower stage screw extruder 2 by the pair of right and left feed rollers 921. The ceramic material 80 is moved forward while being further kneaded in the screw extruder 2, and is extruded from the extrusion molding die 11 through a resisting pipe 12 to obtain the ceramic molding 8.
The extrusion molding machine of the prior art mentioned above has the following drawbacks.
Namely, to enhance the productivity by increasing the molding speed in the extrusion molding machine 9, it is necessary to increase the amount of the ceramic material 80 to be charged in the material introduction portion 93 per unit time and to increase the rotation speed of the feed rollers 931.
However, the material introduction portion 93 can respond only to a certain amount of increase in the amount of the material to be fed, so that feed of the ceramic material 80 into the screw extruder 3 may be stopped. Concretely, if a large amount of the ceramic material 80 is charged in the material introduction portion 93, the feed rollers 931 having projections and depressions idle-rotate with the surfaces thereof having part of the ceramic material stuck thereto. Consequently, as can be seen in FIG. 18, the ceramic material 80 cannot be fed downward and deposit of the ceramic material 80 can be produced above the feed rollers 931. Therefore, the increase in the molding speed is limited in the conventional extrusion molding machine 9 and, hence, it is difficult to enhance the productivity sufficiently.
One of the reasons can be considered as follows.
Namely, the ceramic material 80 which is not kneaded is charged in the material introduction portion 93 and is usually in a state of mixture of powders of a plurality of ceramic components and water mixed therewith like a clod and contains plenty of air. Thus, the ceramic material 80 in the material introduction portion 93 has a very low bulk density. Therefore, the ceramic material 80 tends not to drop due to the dead weight, thus leading to production of the deposit mentioned above.
It is an object of the present invention to provide an extrusion molding machine for producing a ceramic molding, in which the ceramic material which is not kneaded can be efficiently introduced to increase the molding speed.
To achieve the object mentioned above, according to an embodiment of the present invention, there is provided an extrusion molding machine for producing a ceramic molding, comprising a screw extruder having a housing and an extruding screw incorporated in the housing and provided with a shaft portion and a lead portion spirally wound about the shaft portion, and a material introduction portion which is adapted to introduce a ceramic material into the screw extruder, wherein the material introduction portion is provided with a casing which has an introduction passage connected to the inside of the housing of the screw extruder and an opening through which the ceramic material is charged, and a pair of right and left introduction screws provided in the introduction passage, said introduction screws being provided with lead portions wound in opposite directions and being arranged so that the lead portions are engaged substantially in a non-contact state, said introduction screws being rotated so that the ceramic material is moved in a direction opposite to the opening at the engagement portion.
In this embodiment, one of the significant features resides in that the material introduction portion is comprised of the casing and the pair of introduction screws.
The casing defines therein the introduction passage in which the pair of right and left introduction screws are provided, as mentioned above. The opening of the casing preferably opens at the rear end side of the engagement portion of the right and left introduction screws (side opposite to the feed direction of the introduction screws). With this arrangement, the charged ceramic material can be smoothly fed to the introduction screws. The position of the material introduction portion can be modified in various ways as explained later.
The effects of the embodiment of the invention will be discussed below.
The extrusion molding machine according to the embodiment of the invention is provided with the material introduction portion constructed as above. Consequently, even if a larger amount of ceramic material is charged in the material introduction portion, the ceramic material can be smoothly fed to the screw extruder. Therefore, the molding speed can be remarkably increased, in comparison with the prior art.
Namely, the material introduction portion is provided with two interengageable introduction screws which are rotated in opposite directions so as to draw and feed the ceramic material therein. Therefore, the ceramic material charged in the engagement portion of the two introduction screws is smoothly fed in a direction opposite to the opening while being loosened by the lead portions of the introduction screws even if the material is not kneaded and has a very low bulk density. The material is forced forwardly by the rotation of the introduction screws. Consequently, the charged ceramic material is successively fed in the introduction passage of the casing without being deposited above the introduction screws, and is introduced in the housing of the screw extruder. Therefore, in this embodiment, the amount of material to be charged in the material introduction portion per unit time can be remarkably increased, in comparison with the prior art.
As may be understood from the foregoing, according to the present invention, an extrusion molding machine for producing a ceramic molding in which the ceramic material which has not been kneaded can be effectively introduced to obtain high molding speed can be provided.
In a preferred embodiment of the invention, each pair of introduction screws is in the form of a cone whose diameter is gradually reduced toward the front end thereof. With this structure, the introduction passage may be gradually reduced in volume toward the front end, i.e., toward the screw extruders. Consequently, the pressure of the ceramic material to be charged can be increased during passing in the introduction passage. Therefore, the ceramic material can be more smoothly fed to the screw extruders due to the increased pressure.
According to another preferred embodiment of the invention, the lead portions of the introduction screws have pitches of turns which are gradually reduced toward the front ends thereof. In this embodiment, the pressure of the ceramic material can be increased toward the front end of the introduction screws. Therefore, the ceramic material can be more smoothly fed to the screw extruder.
In a preferred embodiment of the invention, the introduction passage of the material introduction portion is connected to the inside of the housing at a side portion of the screw extruder. In this embodiment, it is possible to arrange the introduction passage and the introduction screws substantially in the horizontal direction. Furthermore, the front ends of the introduction screws can be located close to the screw extruders. Consequently, a drawback such as pressure drop can be restricted.
The introduction passage of the material introduction portion can be connected to the inside of the housing at an upper portion of the screw extruder. In this arrangement, the freedom of design of the positional relationship between the material introduction portion and the screw extruders can be enhanced. This arrangement could contribute to reduction of the necessary accommodation space.
In a preferred embodiment, the width W of the opening of the introduction passage connected to the housing of the screw extruder is not less than pitch P of the adjacent threads of the lead portions of the extruding screws. Consequently, the transfer of the ceramic material from the introduction passage to the extruding screws can be smoothly carried out.
According to another aspect of the invention, there is provided an extrusion molding machine for producing a ceramic molding, comprising a screw extruder having a housing and an extruding screw incorporated in the housing and provided with a shaft portion and a lead portion spirally wound about the shaft portion, and a material introduction portion which is adapted to introduce a ceramic material into the screw extruder, wherein the material introduction portion is provided with a casing which has an introduction passage connected to the inside of the housing of the screw extruder and an opening through which the ceramic material is charged, and a single introduction screw provided in the introduction passage, the introduction screw being in the form of a cone whose diameter is gradually reduced toward the front end thereof and being provided with a lead portion wound in a direction opposite to the lead portion of the extruding screw, the introduction screw being arranged, so that the lead portion of the introduction screw is engaged by the lead portion of the extruding screw substantially in a non-contact state, the introduction screw and extruding screw being rotated so that the ceramic material is moved in a direction opposite to the opening at the engagement portion.
One of the most significant features of this embodiment resides in that the single introduction screw having a special shape constitutes, in combination with the extruding screw of the screw extruder, the material introduction portion.
With this embodiment, the same effects as those expected from the use of the two introduction screws mentioned above can be obtained. The single introduction screw makes the material introduction portion simple and compact. Note that in this embodiment, the effective length of the extruding screw of the screw extruder is resultingly shortened and, hence, designs should be made taking this point into account.
In a preferred embodiment of the invention, the ceramic material is a material of which cordierite is made. The ceramic material of which cordierite is made is a mixture of power of the components and an appropriate amount of moisture. In the mixture, before kneaded, the powder and the moisture are mixed in a clod state, and the mixture contains a large amount of air. Therefore, the bulk density of the mixture is very low. Consequently, in the case that the material of which cordierite is made is extruded, the above-mentioned effects can be effectively brought out.
In a preferred embodiment, baffle members are provided in the introduction passage of the material introduction portion, the baffle members projecting inward from the casing so that the baffle members are located between the threads of the lead portions of the introduction screw. In this embodiment, the baffle members can scrape the ceramic material existing between the lead portions. Consequently, it is possible to prevent the ceramic material from remaining between the lead portions. Thus, the ceramic material can be certainly fed forward.
The baffle members can be of any shape, and are in the form of, for example, a circular rod or a square rod, etc. The baffle members can be made of various materials, such as a flexible rubber or highly rigid metal.
In another preferred embodiment of the invention, assuming that the height of the threads of the lead portion is H, the overlapping length L of the baffle members and the lead portion, as viewed in the axial direction of the introduction screw, is in the range between 0.1 H and 0.8 H. If L is smaller than 0.1 H, there is a possibility that no effect of the baffle members to scrape the ceramic material existing between the lead portions can be obtained. If L is greater than 0.8 H, there is a possibility that the propelling force for moving the ceramic material caused by the rotation of the introduction screw is reduced.
In a preferred embodiment of the invention, the baffle members are spaced at a distance equal to the pitch of the adjacent threads of the lead portion. With this arrangement, ceramic material existing between the lead portions can be more certainly scraped.